Transitions from a microstrip transmission line to a coaxial line have become common structures in microwave and high frequency systems. These transitions, however, particularly very sharp or right-angle transitions, can be problematic because microwave and high frequency energy prefers to travel in a straight path. When the microstrip or coaxial transmission line has a bend or impedance discontinuity, undesirable energy reflection and radiation takes place. These reflections degrade the signal by effectively reducing the transfer of energy from the signal source to the receiving circuit. Prior art techniques used to minimize these reflections in very sharp and right-angle transitions have included impedance matching and gradual field transitions.
The primary source of the impedance discontinuity in a right-angle coaxial-to-microstrip transition is the parasitic inductance in the signal conduction path and the ground path. The signal conduction path inductance is due to the position of the center conductor pin of the coaxial line above the floor of the coaxial line housing necessary to make the connection to the microstrip line. The signal conduction path inductance is also caused by the length of bond wire necessary to connect the microstrip line to the center conductor pin of the coaxial line. The ground path inductance of a right-angle coaxial-to-microstrip transition is caused by the distance between the end of the ground path of the microstrip line and the end of the ground path of the coaxial line.
Thus a need has arisen for a right-angle coaxial-to-microstrip transition that more effectively reduces the impedance discontinuity and parasitic inductance of the transition. The improved transition should result in a low insertion loss and low reflection loss at the transition operating over a very wide frequency band.